Estimating the thermodynamic contribution of post-industrial warming to recent Greenland ice sheet surface mass loss

Abstract. The pronounced increase in meltwater runoff from the Greenland Ice Sheet in recent decades represents an important source of global sea-level rise. The role of anomalous anticyclonic circulation patterns in facilitating this increase has been widely documented; however, this change in atmospheric circulation has coincided with a rapidly warming Arctic. While amplified Arctic warming has undoubtedly contributed to trends in Greenland's mass loss, the contribution of this shift in background conditions relative to changes in regional circulation patterns has yet to be quantified. Here, we apply the pseudo-global warming method of dynamical downscaling to estimate the contribution of the change in the thermodynamic background state under global warming to observed Greenland Ice Sheet surface mass loss since the turn of the century. Our analysis demonstrates that, had the 2000–2019 sequence of atmospheric circulation occurred under a preindustrial thermodynamic background state, anomalous surface mass loss from the ice sheet would have been reduced by over 62 % relative to observations. We show that the change in the thermodynamic environment under amplified Arctic warming has augmented melt of the ice sheet via longwave radiative effects accompanying an increase in atmospheric water vapor content. Furthermore, the thermodynamic contribution to surface mass loss during the record melt years of 2012 and 2019 was less than half that of the long-term average, suggesting that the pronounced mass loss during those two summers was more a result of the anomalous atmospheric circulation than a direct consequence of the long-term warming trend.